Stands for 'Gordon Freeman Never Wins'.
Gordon freeman is the main Character in Valve's FPS series Halflife, and this term started on Gamefaqs.

The term comes from that fact that on the gamefaqs polls, you could place Gordon against a no-name character and he would still lose the contest.

A theory erupted on the boards that freeman himself never wanted to win, and always kicks ass in the first few hours just to show us that he could win if he realy wanted to; Only to Plumet an lose badly in the last quarter of voting.

p1) Gordon vs. Dagon? Who the hell is Dagon? To bad GFNW- looks like Dagon will get it.